In order to cut or drill a brittle workpiece such as stone, brick, concrete, or asphalt, an abrasive material having a higher hardness than the workpiece is needed.
For such an abrasive, artificial diamond particles, natural diamond particles, cubic boron nitride, and tungsten carbide particles are well known. Of these materials, artificial diamond particles are most widely used.
Artificial diamond (hereinafter, also referred to as “diamond”) was invented in the 1950's, and is known as a material having a higher hardness than any other materials on Earth. Due to this property, the diamond is used for a cutting tool, a grinding tool, and the like.
In particular, the diamond is widely used in the stone machining field in association with cutting or grinding a variety of stones such as granite and marble, and in the construction field in association with cutting or grinding concrete structures.
Typically, a cutting tool includes a cutting tip for directly performing a cutting operation, and a body, namely core, for supporting the cutting tip.
Typically, the body has a disc shape. A body having a shape different from the disc shape may be used. For example, a body having a rectilinear shape is used in a gang saw. The gang saw is also called a “frame saw”.
In the gang saw, steel shots and diamond particles are used as abrasive materials. The gang saw is used to cut a large-size granite or marble material into a plate shape.
In the case of a cutting tool having a disc-shaped body, the cutting tool cuts a workpiece while rotating about a rotation axis of the body in one direction.
When a workpiece is cut using the above-mentioned disc-shaped cutting tool, tails are formed behind abrasive particles on the cutting surface. The tails are matrix portions remaining without being worn behind abrasive particles.
The tails support the abrasive particles during the cutting process. Accordingly, it is possible to prevent the abrasive particles from being early separated from the matrix of the cutting tip even when the protruded height of the abrasive particles becomes high.
However, the disc-shaped cutting tool has a limitation in cutting large-size stone materials because it cannot cut a workpiece having a size larger than the radius of the disc, even at a maximum cutting depth.
Furthermore, when a larger disc size is used, loss of the raw material increases greatly because the body and tip should become thicker.
On the other hand, an example of a cutting tool (gang saw) having a horizontal body is illustrated in FIGS. 1 to 3.
As shown in FIGS. 1 to 3, the gang saw 10 includes a frame 11, which swings, a plurality of cutting tips 12 attached to the frame 11 to cut a workpiece 1, and a frame driver 13 for swing the frame 11.
The frame 11 swings about pivots 14, generally two pivot points 14.
As the frame 11 swings, abrasive particles 2 on the cutting surface of each cutting tip 12 perform a cutting operation.
In addition to the abrasive particles 2, which directly cut, each cutting tip 12 includes a matrix for binding the abrasive particles 2.
The cutting process using the gang saw 10 is carried out in such a manner that, when the frame 11 is swung by the frame driver 12, the cutting tips 12 attached to the frame 11 cuts through the workpiece while swing, thereby cutting the workpiece.
In the case of the gang saw 10, the frame thereof can cut through the workpiece during the cutting process. Accordingly, there is an advantage in that it is possible to cut a large-size workpiece irrespective of the size of the workpiece.
Also, the frame can be maintained in a rectilinear state because tensile stress is applied to the frame at opposite ends of the frame. Accordingly, there is an advantage in that the loss of the raw material can be minimized because the cutting tip can be thinner than the cutting tip of the disc shaped cutting tool.
Meanwhile, since the gang saw cuts a workpiece while swing in opposite directions, the gang saw is not divided into front and rear portions. For this reason, there is no tail formed around the abrasive material. As a result, the gang saw has a serious drawback in that abrasive particles may be easily separated from the matrix. This will be described in detail with reference to FIGS. 4A and 4B.
FIGS. 4A and 4B are schematic views for explaining a tail formation mechanism around an abrasive particle in a unidirectional cutting process and in a bidirectional cutting process.
FIG. 4A is a schematic view taken in the thickness direction of a cutting tip, illustrating one abrasive particle and the surrounding thereof on the cutting surface of a disc-shaped cutting tool.
In the case of the disc-shaped cutting tool, a tail 31 of a matrix 3 is well formed behind the abrasive particle 2, as shown in FIG. 4A, because the cutting tool performs a cutting operation while rotating in one direction. Referring to FIG. 4A, it can be seen that the tail 31 supports the abrasive particle 2.
Although the length of the tail 31 depends on the conditions given, it is effective when it corresponds to about 5 times the size of the abrasive particle 2.
FIG. 4B is a schematic view taken in the thickness direction of a cutting tip, illustrating one abrasive particle and the surrounding thereof on the cutting surface of a swing type frame saw.
In the case of the swing type frame saw, a metal matrix 3 around an abrasive particle 2 is worn without being protected by the abrasive particle 2 because the swing type frame saw performs a cutting operation in opposite directions, as shown in FIG. 4B. Referring to FIG. 4B, it can be seen that there is no tail formed around the abrasive particle 2.
When no tail is formed, the force supporting the abrasive particle 2 is weak. As a result, even when a small portion of the abrasive particle 2 is exposed, the abrasive particle 2 may be easily separated. For this reason, the lifespan of the cutting tool is greatly reduced.
Furthermore, the protruded height of the abrasive particle directly participating in the cutting operation is very low, thereby causing a degradation in cutting performance.
As a result, when a hard workpiece such as granite is cut, the expense of the cutting tool increases greatly. For this reason, the swing type frame saw is mainly used to cut marble having a low hardness.
Conventionally, in order to cut a large-size granite, the steel frames work together with a slurry containing steel shoot and lime dispersed in water. In this case, however, there is a drawback in that the lifespan of the cutting tool is reduced.
The swing type frame saw such as the above-mentioned gang saw may be used to cut a large-size granite, as long as the problem of the early separation of abrasive particles is solved to enable an increase in cutting speed.
To this end, active research has been conducted to achieve an enhancement in the binding force between abrasive particles and metal matrix binding the abrasive particles. However, there is no noticeable effect obtained by such research. Furthermore, there is a limitation in applying the effects obtained by such research.